Ovens are typically controllable to cook food in a desired way.
A typical control of an oven may set the temperature, and set the amount of cooking time. This may be done based on cooking instructions. For example, cooking instructions might say “Cook in a 450° oven for 15 to 17 minutes or until cooked through”. A user reads this off a box, sets the oven and time, and then monitors the cooking.
There is uncertainly in the cooking instructions because oven characteristics, e.g, temperatures, vary, and also different climates (humidity, altitude, etc,) may also vary the cooking time.
Toasters for toasting bread have similar issues.